[PATCH 2/3] API for reading the counter in CTR mode

[Stephan Mueller]

The API call allows reading the current counter of the CTR mode. The API
remains internal to libgcrypt and is not exported to external callers.

Signed-off-by: Stephan Mueller <smueller at chronox.de>
---
 cipher/cipher.c  | 10 ++++++++++
 src/gcrypt-int.h |  2 ++
 2 files changed, 12 insertions(+)

diff --git a/cipher/cipher.c b/cipher/cipher.c
index ff3340f..55853da 100644
--- a/cipher/cipher.c
+++ b/cipher/cipher.c
@@ -1117,6 +1117,16 @@ _gcry_cipher_setctr (gcry_cipher_hd_t hd, const void *ctr, size_t ctrlen)
   return 0;
 }
 
+gpg_err_code_t
+_gcry_cipher_getctr (gcry_cipher_hd_t hd, void *ctr, size_t ctrlen)
+{
+  if (ctr && ctrlen == hd->spec->blocksize)
+    memcpy (ctr, hd->u_ctr.ctr, hd->spec->blocksize);
+  else
+    return GPG_ERR_INV_ARG;
+
+  return 0;
+}
 
 gcry_err_code_t
 _gcry_cipher_authenticate (gcry_cipher_hd_t hd, const void *abuf,
diff --git a/src/gcrypt-int.h b/src/gcrypt-int.h
index 729f54a..ef5337b 100644
--- a/src/gcrypt-int.h
+++ b/src/gcrypt-int.h
@@ -77,6 +77,8 @@ gpg_err_code_t _gcry_cipher_checktag (gcry_cipher_hd_t hd, const void *intag,
                                       size_t taglen);
 gpg_err_code_t _gcry_cipher_setctr (gcry_cipher_hd_t hd,
                                     const void *ctr, size_t ctrlen);
+gpg_err_code_t _gcry_cipher_getctr (gcry_cipher_hd_t hd,
+                                    void *ctr, size_t ctrlen);
 size_t _gcry_cipher_get_algo_keylen (int algo);
 size_t _gcry_cipher_get_algo_blklen (int algo);
 
-- 
2.9.3